In this proposal structure-based drug design approaches will be used to optimize a series of selective inhibitors of the enzyme methionyl tRNA synthetase from the protozoan parasite Trypanosoma brucei. The long term goal is to arrive at new therapeutics for treating human African trypanosomiasis caused by T. brucei infection. The research will be carried out by a highly experienced research team at the University of Washington consisting of four scientists: Dr. Fan (chemistry), Dr. Buckner (pharmacology and parasitology), Dr. Gelb (pharmacology and chemistry), and Dr. Verlinde (structure-based drug design). The proposed research is based on several key preliminary findings. These include: genetic and chemical validation of methionyl tRNA synthetase as a drug target against T. brucei infection; identification of compounds that inhibit parasite growth a high-nanomolar concentrations; discovery of a molecular scaffold that demonstrates oral bioavailability and excellent membrane permeability with potentially CNS penetration; and inhibitor-bound crystal structures of the target enzyme through collaboration with Dr. Hol at the University of Washington. The proposed work will have two specific aims. One aim is to use structure-based design to guide synthesis of next generation inhibitors of T. brucei methionyl tRNA synthetase with improved potency and metabolic stability while preserving selectivity and membrane permeability. The second aim is to use a set of well-established biological assays to evaluate the newly synthesized compounds in terms of efficacy, pharmacological properties, and toxicity. Pre-defined criteria will be used to pass or fail compounds coming to each biological test, and the results will continually be fed back into the iterative design process. Th potential for drug resistance will also be examined. The goal for this project is to identify one lead and one backup compound that are ready for comprehensive GLP preclinical pharmacology and toxicology studies for further development.